Web materials exhibiting elastic-like behavior

ABSTRACT

A web material which exhibits an elastic-like behavior along at least one axis when subjected to an applied and subsequently released elongation. The web material includes a strainable network having at least two visually distinct regions of the same material composition. The first region undergoes a molecular-level deformation and the second region initially undergoes a substantially geometric deformation when the web material is subjected to an applied elongation in a direction substantially parallel to the axis of elongation.

This is a continuation of application Ser. No. 08/566,203, filed on Dec.1, 1995 now abandoned which is a Division of 08/203,087 Feb. 28, 1994,issued as U.S. Pat. No. 5,518,801 which is a C-I-P of 08/100,958 Aug. 3,1993, now abandoned.

FIELD OF THE INVENTION

The present invention relates to web materials, and more particularly,to such web materials which exhibit an elastic-like behavior in responseto an applied and subsequently released (i.e., cycled) elongation alongat least one axis.

The present invention has further relation to web materials wherein theinherent properties of a given web material, e.g., the resistive forceexerted by the web material to an applied elongation can be modified.Additionally, staged resistive forces, lateral contraction, and/ordirection of elastic-like behavior of conventional web materials canalso be modified and/or provided as desired in web materials of thepresent invention.

Web materials of the present invention have a wide range of potentialuses in both durable and disposable articles, but are particularly wellsuited for use in disposable absorbent articles such as sanitarynapkins, bandages, pantiliners, disposable diapers, incontinent briefs,and the like.

BACKGROUND OF THE INVENTION

Absorbent articles such as sanitary napkins, pantiliners, disposablediapers, incontinent briefs, and bandages are designed to absorb andretain liquid and other discharges from the human body and to preventbody and clothing soiling. Typically, most disposable absorbent articlesare made of materials that will not readily stretch under the forcesthat the absorbent article is normally subjected to when worn. Theinability of the materials comprising the absorbent article to stretchwhen subjected to normal wearing forces causes the absorbent article tohave certain drawbacks. One drawback is the lack of comfort for thewearer. The wearer should ideally be able to notice a difference betweenan absorbent article that stretches to conform to the wearer's body withthe wearer's movements and an absorbent article that fails to stretch.For example, a conventional prior art sanitary napkin does not move withthe wearer's undergarments, thereby causing the sanitary napkin to shiftwhich may cause a degree of discomfort for the wearer. Enabling all or aportion of a sanitary napkin to stretch under normal wearing conditionsand forces will permit the sanitary napkin to better conform to thewearer's undergarment and stay in place even when the wearer moves.

Several attempts have been made to make one or more components ofabsorbent articles stretchable in response to relatively low wearingforces. Typical prior art solutions rely on the addition of traditionalelastics such as natural or synthetic rubber. For example, traditionalelastics have been secured to portions of the topsheet and/or backsheetof absorbent articles, such as the waist portion of a disposable diaper,to provide a better fit and overall comfort for the wearer. However,traditional elastics are costly and require a certain degree ofmanipulation and handling during assembly. While traditional elastics doprovide a degree of stretch for the absorbent article, the materials towhich the traditional elastic is secured are typically not normallyconsidered elastic or stretchable. Therefore, the added traditionalelastics must be prestretched prior to being secured to the material orthe material must be subjected to mechanical processing, e.g., ringrolling, to permanently elongate the material to extend beyond itsinitial untensioned length and allow the added traditional elastic to beeffective. Otherwise, the added traditional elastic is restrained by thematerial and is rendered inoperable. An example of an absorbent articlehaving a web material which has been subjected to additional processingto allow the web material to more easily extend with the addedtraditional elastic member is disclosed in U.S. Pat. No. 5,151,092issued to Buell et al. on Sep. 29, 1992 and hereby incorporated hereinby reference. The Buell patent describes an operation which prestrains abacksheet so that the backsheet will, upon mechanical stretching, bepermanently elongated and not fully return to its original undistortedconfiguration. Buell teaches that a traditional elastic member must beadded to the prestrained backsheet material for the invention to beoperable. Buell also discloses that a prestrained backsheet improves theextension and the heat-shrink contraction of the added traditionalelastic member.

Accordingly, it is an object of the present invention to provide webmaterials which exhibit an "elastic-like" behavior in the direction ofapplied elongation without the use of added traditional elastic. As usedherein, the term "elastic-like" describes the behavior of web materialswhich when subjected to an applied elongation, the web materials extendin the direction of applied elongation and when the applied elongationis released the web materials return, to a substantial degree, to theiruntensioned condition. While such web materials exhibiting anelastic-like behavior have a wide range of utility, e.g. durablearticles of apparel, disposable articles of apparel, covering materialssuch as upholstery, wrapping materials for complex shapes and the like,they are particularly well suited for use as a topsheet, a backsheet,and/or an absorbent core in an absorbent article.

SUMMARY OF THE INVENTION

The present invention pertains, in a preferred embodiment, to a webmaterial which exhibits an elastic-like behavior in response to anapplied and subsequently released elongation without the addition oftraditional elastic materials such as natural or synthetic rubber.

Another elastic-like behavior that the web material of the presentinvention may exhibit is an initial elongation and partial recoverywhich results in the web material not returning to its untensionedlength, i.e., the web material has undergone a degree of permanent setor deformation and has a new longer untensioned length. The web materialmay exhibit an elastic-like behavior in response to subsequentelongations of the web material beyond the new longer untensionedlength.

Another elastic-like behavior that can be exhibited is an elongation andrecovery with a definite and sudden increase in the force resistingelongation where this definite and sudden increase in resistive forcerestricts further elongation against relatively small elongation forces.The definite and sudden increase in the force resisting elongation isreferred to as a "force wall". As used herein, the term "force wall"refers to the behavior of the resistive force of a web material duringelongation wherein at some point in the elongation, distinct from theuntensioned or starting point, the force resisting the appliedelongation suddenly increases. After reaching the force wall, additionalelongation of the web material is only accomplished via an increase inthe elongation force to overcome the higher resistive force of the webmaterial.

The web material of the present invention includes a strainable networkhaving at least two visually distinct and dissimilar regions comprisedof the same material composition. The first region is orientedsubstantially parallel to an axis of elongation such that it willundergo a molecular-level deformation in response to an applied axialelongation in a direction substantially parallel to the axis before asubstantial portion of the second region undergoes any substantialmolecular-level deformation. As used herein, the term "substantiallyparallel" refers to an orientation between two axes whereby thesubtended angle formed by the two axes or an extension of the two axesis less than 45°. In the case of a curvilinear element it may be moreconvenient to use a linear axis which represents an average of thecurvilinear element. The second regions initially undergo asubstantially geometric deformation in response to an applied elongationin a direction substantially parallel to the axis.

In a particularly preferred embodiment, the second region is comprisedof a plurality of raised rib-like elements. As used herein, the term"rib-like element" refers to an embossment, debossment or combinationthereof which has a major axis and a minor axis. Preferably, the majoraxis is at least as long as the minor axis. The major axes of therib-like elements are preferably oriented substantially perpendicular tothe axis of applied elongation. The major axis and the minor axis of therib-like elements may each be linear, curvilinear or a combination oflinear and curvilinear. As used herein, the term "substantiallyperpendicular" refers to an orientation between two axes whereby thesubtended angle formed by the two axes or an extension of the two axesis greater than 45°. In the case of a curvilinear element it may be moreconvenient to use a linear axis which represents an average of thecurvilinear element.

The rib-like elements allow the second region to undergo a substantially"geometric deformation" which results in significantly less resistiveforces to an applied elongation than that exhibited by the"molecular-level deformation" of the first region. As used herein, theterm "molecular-level deformation" refers to deformation which occurs ona molecular level and is not discernible to the normal naked eye. Thatis, even though one may be able to discern the effect of molecular-leveldeformation, e.g., elongation of the web material, one is not able todiscern the deformation which allows or causes it to happen. This is incontrast to the term "geometric deformation". As used herein the term"geometric deformation" refers to deformations of the web material whichare discernible to the normal naked eye when the web material orarticles embodying the web material are subjected to an appliedelongation. Types of geometric deformation include, but are not limitedto bending, unfolding, and rotating.

Yet another elastic-like behavior that the web material of the presentinvention may exhibit is an elongation and recovery with two or moresignificantly different force walls. This type of elastic-like behaviorwould be experienced if for example, after reaching a first force wall,sufficient elongation force was applied to overcome the first force walland continue to elongate the web until a second force wall wasencountered.

When the web material of the present invention has multiple or stagedforce walls, rib-like elements in one or more of the second regionsreach their limit of geometric deformation and become essentiallycoplanar with the material in the first region, thereby causing the webmaterial to exhibit a first force wall. Further elongation of the webmaterial molecularly deforms the rib-like elements which have reachedtheir limit of geometric deformation, and simultaneously geometricallydeforms the rib-like elements in the remaining second regions until theyreach their limit of geometric deformation thereby causing the webmaterial to exhibit a second force wall.

In another preferred embodiment, the web material of the presentinvention exhibits at least two significantly different stages ofresistive force to an applied elongation along at least one axis whensubjected to an applied elongation in a direction substantially parallelto the axis. The web material includes a strainable network having atleast two visually distinct regions. One of the regions is configuredsuch that it will exhibit resistive forces in response to an appliedaxial elongation in a direction substantially parallel to the axisbefore a substantial portion of the other region develops anysignificant resistive force to the applied elongation. At least one ofthe regions has a surface-pathlength which is greater than that of theother region as measured substantially parallel to the axis while thematerial is in an untensioned condition. The region exhibiting thelonger surface-pathlength includes one or more rib-like elements whichextend beyond the plane of the other region. The web material exhibitsfirst resistive forces to the applied elongation until the elongation ofthe web material is sufficient to cause a substantial portion of theregion having the longer surface-pathlength to enter the plane ofapplied elongation, whereupon the web of material exhibits secondresistive forces to further elongation. The total resistive force toelongation is higher than the first resistive force to elongationprovided by the first region.

Preferably, the first region has a first surface-pathlength, L1, asmeasured substantially parallel to the axis of elongation while the webmaterial is in an untensioned condition. The second region has a secondsurface-pathlength, L2, as measured substantially parallel to the axisof elongation while the web is in an untensioned condition. The firstsurface-pathlength, L1, is less than the second surface-pathlength, L2.The first region preferably has an elastic modulus, E1, and across-sectional area, A1. The first region produces by itself aresistive force, P1, due to molecular-level deformation in response toan applied axial elongation, D. The second region preferably has anelastic modulus, E2, and a cross-sectional area, A2. The second regionproduces a resistive force, P2, due to geometric deformation in responseto the applied axial elongation, D. The resistive force, P1, issignificantly greater than the resistive force, P2, so long as (L1+D) isless than L2.

Preferably, when (L1+D) is less than L2 the first region provides aninitial resistive force, P1, in response to the applied axialelongation, D, substantially satisfying the equation P1=(A1×E1×DVL1.When (L1+D) is greater than L2 the first and second regions provide atotal resistive force, PT, to the applied axial elongation, D,satisfying the equation. ##EQU1##

In another preferred embodiment, the web material exhibits a Poissonlateral contraction effect less than about 0.4 at 20% elongation asmeasured perpendicular to the axis of elongation. As used herein, theterm "Poisson lateral contraction effect" describes the lateralcontraction behavior of a material which is being subjected to anapplied elongation. Preferably, the web material exhibits a Poissonlateral contraction effect less than about 0.4 at 60% elongation asmeasured perpendicular to the axis of elongation.

Preferably, the surface-pathlength of the second region is at leastabout 15% greater than that of the first region as measured parallel tothe axis of elongation while the web material is in an untensionedcondition. More preferably, the surface-pathlength of the second regionis at least about 30% greater than that of the first region as measuredparallel to the axis of elongation while the web is in an untensionedcondition.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the present invention, it is believed that thepresent invention will be better understood from the followingdescription in conjunction with the accompanying drawings, in which likereference numerals identify like elements and wherein:

FIG. 1 is a simplified plan view illustration of a prior art sanitarynapkin with portions cut-away to more clearly show the construction ofthe sanitary napkin;

FIG. 2 is a simplified plan view illustration of a prior art disposablediaper with portions cut-away to more clearly show the construction ofthe disposable diaper;

FIG. 3 is a plan view photograph of a prior art deeply embossedpolymeric web with the embossments facing away from the viewer;

FIG. 4 is a graph of the resistive force versus percent elongation ofthe prior art deeply embossed web of FIG. 3;

FIG. 5 is a plan view photograph of a preferred embodiment of apolymeric web material having a first region and a second region of thepresent invention with the rib-like elements of the second region facingtoward the viewer;

FIG. 5A is a segmented, perspective illustration of the polymeric webmaterial of FIG. 5 in an untensioned condition;

FIG. 5B is a segmented, perspective illustration of a polymeric webmaterial of FIG. 5 in a tensioned condition corresponding to stage I onthe force-elongation curve depicted in FIG. 6;

FIG. 5C is a segmented perspective illustration of the polymeric webmaterial of FIG. 5 in a tensioned condition corresponding to stage II onthe force-elongation curve depicted in FIG. 6;

FIG. 6 is a graph of the resistive force versus percent elongationcomparing the behavior of a web material of the present invention, asshown in FIG. 5, formed from Clopay 1401, with a base web of similarmaterial composition;

FIG. 7 is a graph of the elastic hysteresis behavior of the web materialof the present invention which is graphically represented by curve 720in FIG. 6 when the web material is subjected to a hysteresis test at 60%elongation;

FIG. 8 is a graph of the resistive force versus percent elongationcomparing the behavior of a web material of the present invention formedfrom Tredegar sample P-8863/X8323, with a base web of similar materialcomposition;

FIG. 9 is a graph of the elastic hysteresis behavior of the web materialof the present invention which is graphically represented by curve 750in FIG. 8 when the web material is subjected to a hysteresis test at 60%elongation;

FIG. 10 is a graph of the resistive force versus percent elongationcomparing the behavior of another web material of the present inventionformed from, Tredegar sample X-8998, with a base web of similar materialcomposition;

FIG. 11 is a graph of the elastic hysteresis behavior of the webmaterial of the present invention which is graphically represented bycurve 780 in FIG. 10 when the web material is subjected to a hysteresistest at 60% elongation;

FIG. 12 is a graph of the resistive force versus percent elongationcomparing the behavior of another web material of the present inventionformed from, Volara 2A foam sheet, with a base web of similar materialcomposition;

FIG. 13 is a graph of the elastic hysteresis behavior of the webmaterial of the present invention which is graphically represented bycurve 810 in FIG. 12 when the web material is subjected to a hysteresistest at 60% elongation;

FIG. 14 is a graph of the resistive force versus percent elongationcomparing the behavior of another web material of the present inventionformed from a laminate comprised of layer of the Clopay 1401 film,Findley adhesive 2301, and a Veratec P-11 nonwoven layer, with a baseweb of similar material composition;

FIG. 15 is a graph of the elastic hysteresis behavior of the webmaterial of the present invention which is graphically represented bycurve 840 in FIG. 14 when the web material is subjected to a hysteresistest at 60% elongation;

FIGS. 16-29 are illustrations of other preferred embodiments of webmaterials of the present invention;

FIG. 30 is a plan view illustration of a disposable diaper backsheet ofthe present invention;

FIG. 31 is a plan view illustration of a sanitary napkin backsheet ofthe present invention;

FIG. 32 is a simplified side elevational view of a preferred apparatusused to form web materials of the present invention;

FIG. 33 is a plan view of the opposed meshing plates of the apparatus ofFIG. 32 laid side-by-side with their meshing surfaces exposed;

FIG. 34 is a simplified side elevational view of a static press used toform web materials of the present invention;

FIG. 35 is a simplified side elevational view of a continuous, dynamicpress used to form web materials of the present invention;

FIG. 36 is a simplified illustration of another apparatus used to formweb materials of the present invention;

FIG. 37 is a simplified illustration of yet another apparatus used toform web materials of the present invention; and

FIG. 38 is a photomicrograph of an "edge on" view of the second regionused to determine the surface pathlength L2.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term "absorbent article" refers to devices whichabsorb and contain body exudates, and, more specifically, refers todevices which are placed against or in proximity to the body of thewearer to absorb and contain the various exudates discharged from thebody. The term "absorbent article" is intended to include diapers,catamenial pads, sanitary napkins, pantiliners, incontinent briefs,bandages, and the like. The term "disposable" is used herein to describeabsorbent articles which are not intended to be laundered or otherwiserestored or reused as an absorbent article (i.e., they are intended tobe discarded after a single use, and, preferably, to be recycled,composed or otherwise disposed of in an environmentally compatiblemanner). Because of their single use nature, low cost materials andmethods of construction are highly desirable in disposable absorbentarticles.

FIG. 1 is a plan view of a prior art sanitary napkin 20 with portions ofthe structure being cut-away to more clearly show the construction ofthe sanitary napkin 20 and with the portion of the sanitary napkin 20which faces away from the wearer, i.e., the outer surface, orientedtowards the viewer. As used herein, the term "sanitary napkin" refers toan absorbent article which is worn by females adjacent to the pudendalregion, generally external to the urogenital region, and which isintended to absorb and contain menstrual fluids and other vaginaldischarges from the wearer's body (e.g., blood, menses, and urine). Asshown in FIG. 1, the sanitary napkin 20 comprises a liquid pervioustopsheet 24, a liquid impervious backsheet 26 joined with the topsheet24, and an absorbent core 28 positioned between the topsheet 24 and thebacksheet 26.

While the topsheet, backsheet, and absorbent core may be assembled in avariety of well known configurations (including so called "tube"products or side flap products), preferred sanitary napkinconfigurations are described generally in U.S. Pat. No. 4,950,264,issued to Osborn on Aug. 21, 1990; U.S. Pat. No. 4,425,130, issued toDesMarais on Jan. 10, 1984; U.S. Pat. No. 4,321,924, issued to Ahr onMar. 30, 1982; and U.S. Pat. No. 4,589,876, issued to Van Tilburg onAug. 18, 1987. Each of these patents are hereby incorporated herein byreference.

FIG. 2 is a plan view of a prior art disposable diaper 30 in itsuncontracted state (i.e., with elastic induced contraction pulled outexcept in the side panel wherein the elastic is left in its relaxedcondition) with portions of the structure being cut-away to more clearlyshow the construction of the diaper 30 and with the portion of thediaper 30 which faces away from the wearer, i.e., the outer surface,oriented towards the viewer. As used herein, the term "diaper" refers toan absorbent article generally worn by infants and incontinent personsthat is worn about the lower torso of the wearer. As shown in FIG. 2,the diaper 30 comprises a liquid pervious topsheet 34, a liquidimpervious backsheet 36 joined with the topsheet 34, an absorbent core38 positioned between the topsheet 34 and the backsheet 36, elasticizedside panels 40, elasticized leg cuffs 42, an elastic waist feature 44,and a fastening system generally multiply designated as 46.

While the diaper 30 may be assembled in a variety of well knownconfigurations, preferred diaper configurations are described generallyin U.S. Pat. No. 3,860,003, issued to Kenneth B. Buell on Jan. 14, 1975;and U.S. Pat. No. 5,151,092 issued to Kenneth B. Buell et al. on Sep.29, 1992. Each of these patents are hereby incorporated herein byreference.

While the present invention will be described in the content ofproviding a "web material" which exhibits elastic-like behavior to anapplied and subsequently released elongation which is particularly wellsuited for use as a backsheet, a topsheet and/or an absorbent core or aportion thereof on a disposable absorbent article such as a disposablediaper, sanitary napkin, or bandage the present invention is in no waylimited to such application. It may be employed in nearly anyapplication where a relatively low cost elastic-like web material isdesired, e.g., durable articles of apparel, such as exercise clothing,disposable articles of apparel, elastic bandages, upholstery or wrappingmaterial used to cover complex shaped articles, etc. As used herein theterm "web material" refers to a sheet-like material, e.g., a topsheet,backsheet, or absorbent core on a disposable absorbent article, acomposite or laminate of two or more sheet-like materials and the like.The present invention may be practiced to great advantage in manysituations where it is desirable to produce a web material whichexhibits an elastic-like behavior to an applied and subsequentlyreleased elongation along at least one axis. The detailed description ofa preferred structure and its use as a backsheet on a sanitary napkin ora disposable diaper will allow one skilled in the art to readily adaptthe present invention to other applications.

FIG. 3 is a plan view photograph of a prior art deeply embossedpolymeric web 47 which has been used as a backsheet on prior artabsorbent articles. Specifically, the deeply embossed web 47 isavailable from Tredegar Film Products, Terra Haute, Ind. under thedesignation ULAB X-5430. The deeply embossed web 47 comprises a patternof embossments 48. FIG. 4 is a resistive force-elongation curve 700 ofthe deeply embossed polymeric web 47 of FIG. 3. The method of generatingthe resistive force-elongation curve 700 can be found in the TestMethods section set forth in subsequent portions of the presentspecification. As can be seen in FIG. 4, the deeply embossed web 47 hasa resistive force-elongation curve 700 which is substantially the sameshape as the resistive force-elongation curve 710, shown in FIG. 6, of atypical unembossed web of similar composition; that is, the resistiveforce-elongation curve 700 follows a substantially single stage,continuous curve in which the force increases steeply and at asubstantially uniform rate until beginning to yield. Thus, it is clearthat this pattern of embossments 48 in web 47 do not significantly alterthe resistive force-elongation properties of the deeply embossed web 47as compared to an unembossed base web of similar material composition.

Despite widespread use of the prior art deeply embossed polymeric web 47as a backsheet on disposable absorbent articles, the deeply embossedpolymeric web does not offer any functionally enhanced properties whencompared to an unembossed base web, i.e., improved conformance, stretchbehavior and/or garment-like fit. This is believed due to the fact thatthe resistive force versus elongation characteristics of the deeplyembossed web are not significantly different than those of an otherwiseidentical planar, base web, i.e., both webs exhibit a substantiallysingle stage higher resistive force versus elongation curve of the typegenerally shown in FIG. 4.

Referring now to FIG. 5, there is shown a preferred embodiment of apolymeric web material 52 of the present invention. The web material 52is shown in FIG. 5 in its substantially untensioned condition. The webmaterial 52 is particularly well suited for use as a backsheet on anabsorbent article, such as the sanitary napkin 20 in FIG. 1 or thedisposable diaper 30 in FIG. 2. The web material 52 has two centerlines,a longitudinal centerline, which is also referred to hereinafter as anaxis, line, or direction "l" and a transverse of lateral centerline,which is also referred to hereinafter as an axis, line, or direction"t". The transverse centerline "t" is generally perpendicular to thelongitudinal centerline "l".

Referring now to FIGS. 5 and 5A, web material 52 includes a "strainablenetwork" of distinct regions. As used herein, the term "strainablenetwork" refers to an interconnected and interrelated group of regionswhich are able to be extended to some useful degree in a predetermineddirection providing the web material with an elastic-like behavior inresponse to an applied and subsequently released elongation. Thestrainable network includes at least a first region 64 and a secondregion 66. Web material 52 includes a transitional region 65 which is atthe interface between the first region 64 and the second region 66. Thetransitional region 65 will exhibit complex combinations of the behaviorof both the first region and the second region. It is recognized thatevery embodiment of the present invention will have a transitionalregion, however, the present invention is defined by the behavior of theweb material in the first region 64 and the second region 66. Therefore,the ensuing description of the present invention will be concerned withthe behavior of the web material in the first regions and the secondregions only since it is not dependent upon the complex behavior of theweb material in the transitional regions 65.

Web material 52 has a first surface 52a and an opposing second surface52b. In the preferred embodiment shown in FIGS. 5 and 5A, the strainablenetwork includes a plurality of first regions 64 and a plurality ofsecond regions 66. The first regions 64 have a first axis 68 and asecond axis 69, wherein the first axis 68 is preferably longer than thesecond axis 69. The first axis 68 of the first region 64 issubstantially parallel to the longitudinal axis of the web material 52while the second axis 69 is substantially parallel to the transverseaxis of the web material 52. Preferably, the second axis of the firstregion, the width of the first region, is from about 0.01 inches toabout 0.5 inches, and more preferably from about 0.03 inches to about0.25 inches. The second regions 66 have a first axis 70 and a secondaxis 71. The first axis 70 is substantially parallel to the longitudinalaxis of the web material 52, while the second axis 71 is substantiallyparallel to the transverse axis of the web material 52. Preferably, thesecond axis of the second region, the width of the second region, isfrom about 0.01 inches to about 2.0 inches, and more preferably fromabout 0.125 inches to about 1.0 inches. In the preferred embodiment ofFIG. 5, the first regions 64 and the second regions 66 are substantiallylinear, extending continuously in a direction substantially parallel tothe longitudinal axis of the web material 52.

The first region 64 has an elastic modulus E1 and a cross-sectional areaA1. The second region 66 has a modulus E2 and a cross-sectional area A2.

In the illustrated embodiment, the web material 52 has been "formed"such that the web material 52 exhibits a resistive force along an axis,which in the case of the illustrated embodiment is substantiallyparallel to the longitudinal axis of the web, when subjected to anapplied axial elongation in a direction substantially parallel to thelongitudinal axis. As used herein, the term "formed" refers to thecreation of a desired structure or geometry upon a web material thatwill substantially retain the desired structure or geometry when it isnot subjected to any externally applied elongations or forces. A webmaterial of the present invention is comprised of at least a firstregion and a second region, wherein the first region is visuallydistinct from the second region. As used herein, the term "visuallydistinct" refers to features of the web material which are readilydiscernible to the normal naked eye when the web material or objectsembodying the web material are subjected to normal use. As used hereinthe term "surface-pathlength" refers to a measurement along thetopographic surface of the region in question in a directionsubstantially parallel to an axis. The method for determining thesurface-pathlength of the respective regions can be found in the TestMethods section set forth in subsequent portions of the presentspecification.

Methods for forming web materials of the present invention include, butare not limited to embossing by mating plates or rolls, thermoforming,high pressure hydraulic forming, or casting. While the entire portion ofthe web 52 has been subjected to a forming operation, the presentinvention may also be practiced by subjecting to formation only aportion thereof, e.g., a portion of a diaper backsheet, as will bedescribed in detail below.

In the preferred embodiment shown in FIGS. 5 and 5A, the first regions64 are substantially planar. That is, the material within the firstregion 64 is in substantially the same condition before and after theformation step undergone by web 52. The second regions 66 include aplurality of raised rib-like elements 74. The rib-like elements may beembossed, debossed or a combination thereof. The rib-like elements 74have a first or major axis 76 which is substantially parallel to thetransverse axis of the web 52 and a second or minor axis 77 which issubstantially parallel to the longitudinal axis of the web 52. The firstaxis 76 of the rib-like elements 74 is at least equal to, and preferablylonger than the second axis 77. Preferably, the ratio of the first axis76 to the second axis 77 is at least about 1:1 or greater, and morepreferably at least about 2:1 or greater.

The rib-like elements 74 in the second region 66 may be separated fromone another by unformed areas. Preferably, the rib-like elements 74 areadjacent one another and are separated by an unformed area of less than0.10 inches as measured perpendicular to the major axis 76 of therib-like elements 74, and more preferably, the rib-like elements 74 arecontiguous having no unformed areas between them.

The first region 64 and the second region 66 each have a "projectedpathlength". As used herein the term "projected pathlength" refers tothe length of a shadow of a region that would be thrown by parallellight. The projected pathlength of the first region 64 and the projectedpathlength of the second region 66 are equal to one another.

The first region 64 has a surface-pathlength, L1, less than thesurface-pathlength, L2, of the second region 66 as measuredtopographically in a direction parallel to the longitudinal axis of theweb 52 while the web is in an untensioned condition. Preferably, thesurface-pathlength of the second region 66 is at least about 15% greaterthan that of the first region 64, more preferably at least about 30%greater than that of the first region, and most preferably at leastabout 70% greater than that of the first region. In general, the greaterthe surface-pathlength of the second region, the greater will be theelongation of the web before encountering the force wall.

Web material 52 exhibits a modified "Poisson lateral contraction effect"substantially less than that of an otherwise identical base web ofsimilar material composition. The method for determining the Poissonlateral contraction effect of a material can be found in the TestMethods section set forth in subsequent portions of the presentspecification. Preferably, the Poisson lateral contraction effect ofwebs of the present invention is less than about 0.4 when the web issubjected to about 20% elongation. Preferably, the webs exhibit aPoisson lateral contraction effect less than about 0.4 when the web issubjected to about 40, 50 or even 60% elongation. More preferably, thePoisson lateral contraction effect is less than about 0.3 when the webis subjected to 20, 40, 50 or 60% elongation. The Poisson lateralcontraction effect of webs of the present invention is determined by theamount of the web material which is occupied by the first and secondregions, respectively. As the area of the web material occupied by thefirst region increases the Poisson lateral contraction effect alsoincreases. Conversely, as the area of the web material occupied by thesecond region increases the Poisson lateral contraction effectdecreases. Preferably, the percent area of the web material occupied bythe first area is from about 2% to about 90%, and more preferably fromabout 5% to about 50%.

Web materials of the prior art which have at least one layer of anelastomeric material will generally have a large Poisson lateralcontraction effect, i.e., they will "neck down" as they elongate inresponse to an applied force. Web materials of the present invention canbe designed to moderate if not substantially eliminate the Poissonlateral contraction effect.

For web material 52, the direction of applied axial elongation, D,indicated by arrows 80 in FIG. 5, is substantially perpendicular to thefirst axis 76 of the rib-like elements 74. The rib-like elements 74 areable to unbend or geometrically deform in a direction substantiallyperpendicular to their first axis 76 to allow extension in web 52.

In FIG. 6 there is shown a graph of the resistive force-elongation curve720 of a web material generally similar to web material 52 shown in FIG.5 along with a curve 710 of a base film material of similar composition.Specifically the samples are polymeric web materials, comprisedsubstantially of linear low density polyethylene, approximately 0.001"thick, designated sample 1401 available from Clopay, Cincinnati Ohio.The method for generating the resistive force-elongation curves can befound in the Test Methods section set forth in subsequent portions ofthe present specification. Referring now to the force-elongation curve720 of the formed web, there is an initial substantially linear, lowerforce versus elongation stage I designated 720a, a transition zonedesignated 720b which indicates the encounter of the force wall, and asubstantially linear stage II designated 720c which displayssubstantially higher force versus elongation behavior.

As seen in FIG. 6 the formed web exhibits different elongation behaviorin the two stages when subjected to an applied elongation in a directionparallel to the longitudinal axis of the web. The resistive forceexerted by the formed web to the applied elongation is significantlyless in the stage I region (720a) versus the stage II region (720c) ofcurve 720. Furthermore, the resistive force exerted by the formed web tothe applied elongation as depicted in stage I (720a) of curve 720 issignificantly less than the resistive force exerted by the base web asdepicted in curve 710 within the limits of elongation stage I. As theformed web is subjected to further applied elongation and enters stageII (720c) the resistive force exerted by the formed web increases andapproaches the resistive force exerted by the base web. The resistiveforce to the applied elongation for the stage I region (720a) of theformed web is provided by the molecular-level deformation of the firstregion of the formed web and the geometric deformation of the secondregion of the formed web. This is in contrast to the resistive force toan applied elongation that is provided by the base web, depicted incurve 710 of FIG. 6, which results from molecular-level deformation ofthe entire web. Web materials of the present invention can be designedto yield virtually any resistive force in stage I which is less thanthat of the base web material by adjusting the percentage of the websurface which is comprised of the first and second regions,respectively. The force-elongation behavior of stage I can be controlledby adjusting the width, cross-sectional area, and spacing of the firstregion and the composition of the base web.

Referring now to FIG. 5B, as web 52 is subjected to an applied axialelongation, D, indicated by arrows 80 in FIG. 5, the first region 64having the shorter surface-pathlength, L1, provides most of the initialresistive force, P1, as a result of molecular-level deformation, to theapplied elongation which corresponds to stage I. While in stage I, therib-like elements 74 in the second region 66 are experiencing geometricdeformation, or unbending and offer minimal resistance to the appliedelongation. In the transition zone (720b) between stages I and II, therib-like elements 74 are becoming aligned with the applied elongation.That is, the second region is exhibiting a change from geometricdeformation to molecular-level deformation. This is the onset of theforce wall. In stage II, as seen in FIG. 5C, the rib-like elements 74 inthe second region 66 have become substantially aligned with the plane ofapplied elongation (i.e. the second region has reached its limit ofgeometric deformation) and begin to resist further elongation viamolecular-level deformation. The second region 66 now contributes, as aresult of molecular-level deformation, a second resistive force, P2, tofurther applied elongation. The resistive forces to elongation depictedin stage II by both the molecular-level deformation of the first region64 and the molecular-level deformation of the second region 66 provide atotal resistive force, PT, which is greater than the resistive forcedepicted in stage I which is provided by the molecular-level deformationof the first region 64 and the geometric deformation of the secondregion 66. Accordingly, the slope of the force-elongation curve in stageII is significantly greater than the slope of the force-elongation curvein stage I.

The resistive force P1 is substantially greater than the resistive forceP2 when (L1+D) is less than L2. When (L1+D) is less than L2 the firstregion provides the initial resistive force P1, generally satisfying theequation: ##EQU2## When (L1+D) is greater than L2 the first and secondregions provide a combined total resistive force PT to the appliedelongation, D, generally satisfying the equation: ##EQU3##

The maximum elongation occurring while in stage I is the "availablestretch" of the formed web material. The available stretch correspondsto the distance over which the second region experiences geometricdeformation. The available stretch can be effectively determined byinspection of the force-elongation curve 720 as shown in FIG. 6. Theapproximate point at which there is an inflection in the transition zonebetween stage I and stage II is the percent elongation point of"available stretch". The range of available stretch can be varied fromabout 10% to 100% or more; this range of elongation is often found to beof interest in disposable absorbent articles, and can be largelycontrolled by the extent to which the surface-pathlength L2 in thesecond region exceeds the surface-pathlength L1 in the first region andthe composition of the base film. The term available stretch is notintended to imply a limit to the elongation which the web of the presentinvention may be subjected to as there are applications where elongationbeyond the available stretch is desirable.

The curves 730 and 735 in FIG. 7 show the elastic hysteresis behaviorexhibited by a web material of the present invention which is generallysimilar to that used to generate curve 720 in FIG. 6. The formed web wasexamined for elastic hysteresis behavior at an elongation of 60%. Curve730 represents the response to an applied and released elongation duringthe first cycle and curve 735 represent the response to an applied andreleased elongation during the second cycle. The force relaxation duringthe first cycle 731 and the percent set or deformation 732 are depictedin FIG. 7. Note that significant recoverable elongation, or usefulelasticity, is exhibited at relatively low forces over multiple cycles,i.e., the web material can easily expand and contract to a considerabledegree. The method of generating the elastic hysteresis behavior can befound in the Test Method section set forth in subsequent portion of thepresent specification.

FIG. 8 shows the force-elongation behavior for both a base web depictedin curve 740 and a formed web of the present invention depicted in curve750 where both webs are comprised of a linear low density polyethylenefilm, approximately 0.001" thick, available from Tredegar Inc, TerreHaute, Ind., and designated P-8863/X8323. This type of base film hasbeen successfully commercially utilized as a fluid impervious backsheeton disposable diapers. Referring now to curve 750, there is an initialsubstantially linear, lower force-elongation stage I designated 750a, atransition zone designated 750b, and a substantially linear stage IIdesignated 750c. Note the distinctive lower force two-stage behavior inthe formed web provided first in stage I by the combination ofmolecular-level deformation of the first region and geometricdeformation of the second region, and then in stage II bymolecular-level deformation of both the first region and the secondregion as depicted by curve 750 compared to the molecular-leveldeformation of the base web as depicted by curve 740. The curves 760 and765 in FIG. 9 show the elastic hysteresis behavior of a formed websimilar to that used to generate curve 750 in FIG. 8 when examined in60% elongation. Curve 760 represents the response to an applied andreleased elongation during the first cycle and curve 765 represents theresponse to an applied and released elongation during the second cycle.The force relaxation during the first cycle 761 and the percent set ordeformation 762 are depicted in FIG. 9. Note that there is verysignificant elastic recovery exhibited by the sample over this observedrange of elongations over multiple cycles.

FIG. 10 shows the force-elongation behavior for both a base web depictedin curve 770 and a formed web of the present invention depicted in curve780 where both webs are comprised of a think polymeric film,approximately 0.001" thick, consisting mostly of linear medium densitypolyethylene plus linear low density polyethylene, available fromTredegar Inc, Terra Haute, Ind., and designated X-8998. Referring now tocurve 780, there is an initial substantially linear, lowerforce-elongation stage I designated 780a, a transition zone designated780b, and a substantially linear higher force-elongation stage IIdesignated 780c. Note the distinctive lower force two-stage behavior inthe formed web provided first in stage I by the combination ofmolecular-level deformation of the first region and geometricdeformation of the second region and then in stage II molecular-leveldeformation of both the first region and the second region as depictedin curve 780 compared to the molecular-level deformation of the base webas depicted in curve 770. Curves 790 and 795 in FIG. 11 show the elastichysteresis behavior of a formed web material similar to that used togenerate curve 780 in FIG. 10 examined at 60% elongation. Curve 790represents the response to an applied and released elongation during thefirst cycle and curve 795 represents the response to an applied andreleased elongation during the second cycle. The force relaxation of theweb during the first cycle is depicted by 791 and the degree of set ordeformation of the web material after the first cycle is depicted by792. In this example, the web material was elongated to a point wherethe material in the first region which was experiencing molecular-leveldeformation was permanently deformed (i.e., experienced a permanent set)by the elongation. It should further be noted that the 60% elongationthat produced the permanent deformation of the web material in the firstregion was insufficient to encounter the limits of the geometricdeformation of the second region, i.e., the force wall. That is, thelimits of the geometric deformation of the second region was greaterthan the elastic limits of the molecular-level deformation of the firstregion. However, this permanent deformation of the first region did noteliminate useful elastic-like behavior of the web material, but ratherresulted effectively in merely a "shifting" of the untensioned point ofelastic-like behavior of the web material. This is illustrated by curve795 which depicts the behavior of the web material on the second cycle,after permanent deformation. A useful amount of elastic-like behaviorwill remain, even at higher levels of permanent deformation of the typeillustrated by the example in FIG. 11. It is recognized that this usefulelastic-like behavior will diminish at extremely high levels ofelongation of the web material and subsequent high permanent deformationof the material in the first regions of the web.

FIG. 12 shows the force-elongation behavior for both a base web depictedin curve 800 and a formed web of the present invention depicted in curve810 where both webs are comprised of a foam polyethylene sheet,approximately 0.080" thick, available as Volara 2a from Voltek Corp.,Lawrence, Mass. Referring now to curve 810, there is an initialsubstantially linear, lower force-elongation stage I designated 810a, atransition zone designated 810b, and a substantially linear stage IIdesignated 810c. Note the distinctive lower force two-stage behavior inthe formed web provided first in stage I (810a) by the combination ofmolecular-level deformation of the first region and geometricdeformation of the second region and then in stage II (810c) bymolecular-level deformation of both the first region and the secondregion as depicted in curve 810 compared to the molecular-leveldeformation of the base web as depicted in curve 800. Note that the basefoam sample undergoes failure at an elongation less than about 150% andthe formed web undergoes failure at less than about 120% elongation. Thecurves 820 and 825 in FIG. 13 show the elastic hysteresis behavior of aformed web material similar to that used to generate curve 810 in FIG.12 examined at 60% elongation. Curve 820 represents the response to anapplied and released elongation during the first cycle and curve 825represents the response to an applied and released elongation during thesecond cycle. The force relaxation of the web during the first cycle 821and the degree of set of the web after the first cycle 822 are depictedin FIG. 13. Note that this sample displays very significant elasticrecovery over this observed range of elongation as evidenced by thesmall amount of permanent set 822.

FIG. 14 shows the force-elongation behavior for both a base web depictedby curve 830 and a formed web of the present invention depicted by curve840 where both webs are comprised of a laminate of a layer of the Clopay1401 polyethylene blend film adhered via a hot melt glue available fromFindley Adhesives, Wauwatosa, Wis., sample 2301, to a layer of nonwovenlayer, made substantially of polypropylene, available from Veratec,Wolpole, Mass., designated type P-11. Referring now to curve 840, thereis an initial substantially linear, lower force-elongation stage Idesignated 840a, a transition zone designated 840b, and a substantiallylinear stage II designated 840c. For the laminate web, note thedistinctive lower force two-stage behavior in the formed web providedfirst in stage I (840a) by the combination of molecular-leveldeformation of the first region and geometric deformation of the secondregion and then in stage II (840c) by molecular-level deformation ofboth the first region and the second region as depicted in curve 840compared to the molecular-level deformation of the base web as depictedin curve 830. The curves 850 and 855 in FIG. 15 show the elastichysteresis behavior of a formed web material similar to that used togenerate curve 840 in FIG. 14 examined at 60% elongation. Curve 850represents the response to an applied and released elongation during thefirst cycle and curve 855 represents the response to an applied andreleased elongation during the second cycle. The force relaxation of theweb during the first cycle 851 and the percent set of the web after thefirst cycle 852 are shown in FIG. 15. Note that this laminate webexhibits a very significant elastic recovery over the observed range ofelongation over multiple-cycles.

When the web material is subjected to an applied elongation, the webmaterial exhibits an elastic-like behavior as it extends in thedirection of applied elongation and returns to its substantiallyuntensioned condition once the applied elongation is removed, unless theweb material is extended beyond the point of yielding. The web materialis able to undergo multiple cycles of applied elongation without losingits ability to substantially recover. Accordingly, the web is able toreturn to its substantially untensioned condition once the appliedelongation is removed.

While the web material may be easily and reversibly extended in thedirection of applied axial elongation, in a direction substantiallyperpendicular to the first axis of the rib-like elements, the webmaterial is not as easily extended in a direction substantially parallelto the first axis of the rib-like elements. The formation of therib-like elements allows the rib-like elements to geometrically deformin a direction substantially perpendicular to the first or major axis ofthe rib-like elements, while requiring substantially molecular-leveldeformation to extend in a direction substantially parallel to the firstaxis of the rib-like elements.

The amount of applied force required to extend the web is dependent uponthe composition and cross-section area of the web material and the widthand spacing of the first regions, with narrower and more widely spacedfirst regions requiring lower applied extensional forces to achieve thedesired elongation for a given composition and cross-sectional area. Thefirst axis, (i.e., the length) of the first regions is preferablygreater than the second axis, (i.e., the width) of the first regionswith a preferred length to width ratio of from about 5:1 or greater.

The depth and frequency of rib-like elements can also be varied tocontrol the available stretch of a web of the present invention. Theavailable stretch is increased if for a given frequency of rib-likeelements, the height or degree of formation imparted on the rib-likeelements is increased. Similarly, the available stretch is increased iffor a given height or degree of formation, the frequency of the rib-likeelements is increased.

While the particular web material 52 of FIG. 5 is an example of anelastic-like web of the present invention, the present invention is notlimited to the geometric formation shown in web material 52. FIGS. 16-28depict several alternative embodiments of web materials of the presentinvention.

There are several functional properties that can be controlled throughthe application of the present invention. The functional properties arethe resistive force exerted by the web material against an appliedelongation and the available stretch of the web material before theforce wall is encountered. The resistive force that is exerted by theweb material against an applied elongation is a function of the material(e.g., composition, molecular structure and orientation, etc.) andcross-sectional area and the percent of the projected surface area ofthe web material that is occupied by the first region. The higher thepercent area coverage of the web material by the first region, thehigher the resistive force that the web will exert against an appliedelongation for a given material composition and cross-sectional area.The percent coverage of the web material by the first region isdetermined in part if not wholly by the widths of the first regions andthe spacing between adjacent first regions.

The available stretch of the web material is determined by thesurface-pathlength of the second region. This is determined at least inpart by the rib-like element spacing, rib-like element frequency anddepth of formation of the rib-like elements as measured perpendicular tothe plane of the web material. In general, the greater thesurface-pathlength of the second region the greater the availablestretch of the web material.

In FIG. 16 there is shown a formed web material 52a of the presentinvention in an untensioned condition which contains first regions 64aand second regions 66a. Web material 52a also includes transitionalregions 65a located intermediate first regions 64a and second regions66a. The web material 52a will exhibit an elastic-like behavior inresponse to an applied cyclical elongation in a direction along an axisindicated as "l". Second regions 66a contain curvilinear rib-likeelements 74a. The first or major axis 76a of the curvilinear rib-likeelements 74a is a linear approximation of the rib-like element 74a. Themajor axis 76a defines that portion of the rib-like element 74a whichsubstantially responds to an applied elongation via geometricdeformation. In FIG. 17 there is shown the same web material of FIG. 16in a tensioned condition. The tension in the web material, as a resultof the applied elongation indicated by arrows 80a causes the geometricdeformation of rib-like elements 74a in a direction perpendicular to thefirst axis 76a due to the unbending of the rib-like elements 74a.

In FIG. 18 there is shown a formed web material 52b of the presentinvention in an untensioned condition which contains first regions 64band second regions 66b. Web material 52b also includes transitionregions 65b located intermediate first regions 64b and second regions66b. The web material 52b will exhibit an elastic-like behavior inresponse to an applied cyclical elongation in a direction along an axisindicated as "l". Second regions 66b contain complex shaped rib-likeelements 74b. The first or major axis 76b of the rib-like elements 74bare a linear approximation of the rib-like elements 74b. The first ormajor axis 76b defines that portion of the rib-like element 74b whichsubstantially responds to an applied elongation via geometricdeformation. In FIG. 19 there is shown the same formed web material ofFIG. 18 in a tensioned condition. The tension in the web material showsthe geometric deformation of rib-like elements 74b perpendicular to themajor axis 76b due to unbending of the rib-like elements 74b as a resultof the applied elongation indicated by arrows 80b.

In FIG. 20 there is shown another embodiment of a formed web material52c of the present invention in the untensioned condition. Web material52c contains first regions 64c and second regions 66c. Web material 52calso includes transitional regions 65c located intermediate firstregions 64c and second regions 66c. The web material 52c will exhibit anelastic-like behavior in response to an applied cyclical elongation in adirection along an axis indicated as "l". Second region 66c containsrib-like elements 74c. The first regions 64c and the second regions 66care curvilinear. First regions will undergo a substantiallymolecular-level deformation while the second regions will initiallyundergo a substantially geometric deformation when the formed webmaterial 52c is subjected to an applied elongation indicated by arrows80c.

In FIG. 21 there is shown another embodiment of a formed web material52d of the present invention in an untensioned condition. Web material52d contains first regions 64d and second regions 66d. Web material 52dalso includes transitional regions 65d located intermediate firstregions 64d and second regions 66d. Second regions 66d containcurvilinear rib-like elements 74d. The major axis 76d of the curvilinearrib-like elements 74d is a linear approximation of the rib-like elements74d. The major axis 76d defines that portion of the rib-like elements74d which substantially responds to an applied elongation via geometricdeformation. The web material 52d will exhibit an elastic-like behaviorin response to an applied cyclical elongation in a direction along anaxis indicated as "l". The first regions undergo a substantiallymolecular-level deformation and the second regions initially undergo asubstantially geometric deformation when the formed web material 52d issubjected to an applied elongation indicated by arrows 80d.

In FIG. 22 there is shown a web material 52e of the present invention inan untensioned condition which contains first regions 64e and secondregions 66e. Web material 52e also includes transitional regions 65elocated intermediate first regions 64e and second regions 66e. Secondregions 66e contain rib-like elements 74e. The first regions 64e arediscontinuous throughout the length of the web material. The webmaterial 52e will exhibit an elastic-like behavior in response to anapplied cyclical elongation indicated by arrows 80e in a directionsubstantially parallel to axis "l".

In FIG. 23 there is shown a web material 52f of the present invention inan untensioned condition which contains first regions 64f and secondregions 66f. Web material 52f also includes transitional regions 65flocated intermediate first regions 64f and second regions 66f. Secondregions 66f contain rib-like elements 74f. The first regions 64f extendcontinuously throughout the length of the web material while the secondregions 66f are discontinuous or interrupted. The web material of 52fwill exhibit an elastic-like behavior in response to an applied cyclicalelongation indicated by arrows 80f in a direction substantially parallelto axis "l".

In FIG. 24 there is shown a formed web material 52g of the presentinvention in an untensioned condition. Web material 52g contains firstregions 64g and second regions 66g. Web material 52g also includestransitional regions 65g located intermediate first regions 64g andsecond regions 66g. The second regions 66g contain rib-like elements74g. The formed web material 52g exhibits an elastic-like behavior alonga plurality of axis, "l1", "l2" and "l3". Axes l1, l2, and l3, extend ina radial, fan-like array to allow the formed web material 52g to exhibitan elastic-like behavior along a plurality of axes. While web material52g has been shown as having axes extending in a fan-like array, thepresent invention is in no way limited to such. The multiple axes may bepositioned at various angles to one another such as 45°, 90°, 135°, etc.In addition to the various angles of orientation, the regions themselvesmay be straight, curvilinear, or combinations thereof.

In FIG. 25 there is shown a formed web material 52h of the presentinvention. Web material 52h includes first regions 64h and secondregions 66h. Web material 52h also includes transitional regions 65hlocated intermediate first regions 64h and second regions 66h. Secondregion 66h includes a plurality of rib-like elements 74h. In FIG. 25Athere is shown a cross-sectional view of the second region 66h takenalong section-line 25A--25A depicting the amplitudes x and x' of therib-like elements 74h. The surface-pathlength of zone I in second region66h will be substantially less than the surface-pathlength of zone II insecond region 66h at least due in part to a difference in amplitudes xand x' of the rib-like elements 74h in the respective zones. As webmaterial 52h is subjected to an applied elongation indicated by arrows80h in a direction substantially parallel to axis "l", web material willhave different zones of available stretch corresponding to zones I andII in the second regions 66h. Specifically, the available stretch of web52h corresponding to zone I will be less than the available stretch ofweb material 52h corresponding to zone II. However, while the availablestretch for zones I and II are different from one another, web material52h will not encounter a force wall until the available stretch for bothzones I and II has been reached.

In FIG. 26 there is shown a formed web material 52i of the presentinvention. Web material 52i includes first regions 64i and secondregions 66i. Web material 52i also includes transitional regions 65ilocated intermediate first regions 64i and second regions 66i. Secondregions 66i include rib-like elements 74i. FIG. 26A is a cross-sectionalview of the second region 66i taken along section line 26A--26Adepicting the frequencies y and y' of the rib-like elements 74i. Due tothe difference in surface-pathlengths in zones I and II web material 52iof FIGS. 26 and 26A will respond to an applied and released elongationsimilar to web 52h depicted in FIGS. 25 and 25A.

While the web materials in FIGS. 25 and 26 illustrate variations in therib-like elements within a second region one could also vary therib-like elements between adjacent regions. The variations in rib-likeelements in adjacent second regions provides different availablestretches in the adjacent second regions. By having different availablestretches in adjacent second regions the web material will exhibitmultiple force walls in response to an applied elongation as each regionreaches its limit of geometric deformation.

In FIG. 27 there is shown another embodiment of a formed web material52j of the present invention. Web material 52j includes first regions64j and second regions 66j. Web material 52j also includes transitionalregions 65j located intermediate first regions 64j and second regions66j. The widths of the first regions 64 varies across the web in adirection substantially parallel to the axis "t". Second regions 66jinclude a plurality of rib-like elements 74j. As the web material 52j issubjected to an applied elongation indicated by arrows 80j in adirection substantially parallel to the axis "l", the narrower regions64 will offer a lower resistive force to the applied elongation ascompared to the higher resistive force offered by the wider firstregions 64j.

In FIG. 28 there is shown another embodiment of a formed web material52k of the present invention. Web material 52k includes first regions64k and second regions 66k. Web material 52k also includes transitionalregions 65k located intermediate first regions 64k and second regions66k. Second regions 66k include rib-like elements 74k. The widths of thesecond regions 66k varies across the web in a direction substantiallyparallel to axis "t". When subjected to an applied elongation indicatedby arrows 80k in a direction substantially parallel to axis "l" theportions of the web material 52k having the wider second regions 66kwill provide a lower resistive force to the applied elongation ascompared to the portion of web material 52k having the narrower secondregions 66k. It should be obvious to one skilled in the art that thefeatures of the web materials disclosed in FIGS. 27 and 28 can becombined in a single web to provide various resistive forces to appliedelongations.

In FIG. 29 there is shown another embodiment of a web material 521 ofthe present invention. Web material 521 includes first regions 641 andsecond regions 661. Web material 521 also includes transitional regions651 located intermediate first regions 641 and second regions 661.Second regions 661 include rib-like elements 741. Second regions 661extend in a direction substantially parallel to axis "l". The major axis761 of the rib-like elements 741 extends at a slight angle to axis "l"but is still substantially perpendicular to axis "l". As the webmaterial 521 is subjected to an applied elongation indicated by arrows801 in a direction substantially parallel to axis "l" rib-like elements741 will geometrically deform at least in part by pivoting in responseto the applied elongation. The pivoting of rib-like elements 741 maycause the rib-like elements 741 to become aligned substantially parallelwith the axis "l".

While an entire web material of the present invention may include astrainable network of first and second regions, the present inventionmay also be practiced by providing only specific portions of the webwith a strainable network comprised of first and second regions.Referring now to FIG. 30, there is shown a preferred embodiment of adisposable diaper backsheet 200 of the present invention, wherein thebacksheet 200 includes discrete, strainable networks 210 located in thewaist region and the side panels of the disposable diaper backsheet. Itwill be obvious to one skilled in the art that all or a portion of abacksheet on a disposable absorbent article may include a strainablenetwork(s) comprised of first and second regions to provide a backsheetexhibiting an elastic-like behavior along an axis when subjected to anapplied cyclical elongation.

Referring now to FIG. 31, there is shown an embodiment of a sanitarynapkin backsheet 220. The backsheet 220 includes a plurality of firstregions 222 and a plurality of second regions 224 each extending inseveral different directions. Accordingly, the backsheet 220 is able toexhibit elastic-like behavior in several directions to applied cyclicelongations along a plurality of axes.

While the web material having a strainable network of the presentinvention has been described as a backsheet or a portion thereof on anabsorbent article, in some embodiments it may be necessary to providethe topsheet and the absorbent core with a strainable network. Forexample, in the embodiment illustrated in FIG. 30, it is necessary toprovide the topsheet with a strainable network in regions adjacentbacksheet regions 210 to allow region 210 of the backsheet to extendwithout being restrained by adjacent portions of the topsheet.

Method of Making

Referring now to FIG. 32, there is shown an apparatus 400 used to formthe web 52 shown in FIG. 5. Apparatus 400, includes plates 401, 402.Plates 401, 402 include a plurality of intermeshing teeth 403, 404,respectively. Plates 401, 402 are brought together under pressure toform the base film 406.

Referring now to FIG. 33, it can be seen that plates 401 and 402 eachhave a longitudinal axis "l" and a transverse axis "t" which issubstantially perpendicular to the longitudinal axis. Plate 401 includestoothed regions 407 and grooved regions 408 both which extendsubstantially parallel to the longitudinal axis of the plate 401. Withintoothed regions 407 of plate 401 there are a plurality of teeth 403.Plate 402 includes teeth 404 which mesh with teeth 403 of plate 401.When the base film 406 is formed between plates 401, 402 the portions ofthe base film 406 which are positioned within grooved regions 408 ofplate 401 and teeth 404 on plate 402 remain undeformed. These regionscorrespond with the first regions 64 of web 52 shown in FIG. 5. Theportions of the base film 406 positioned between toothed regions 407 ofplate 401 and teeth 404 of plate 402 are incrementally and plasticallyformed creating rib-like elements 74 in the second regions 66 of webmaterial 52.

The method of formation can be accomplished in a static mode, where onediscrete portion of a base film is deformed at a time. An example ofsuch a method is shown in FIG. 34. A static press indicated generally as415 includes an axially moveable plate or member 420 and a stationaryplate 422. Plates 401 and 402 are attached to members 420 and 422,respectively. While plates 401 and 402 are separated, base film 406 isintroduced between the plates, 401, 402. The plates are then broughttogether under a pressure indicated generally as "P". The upper plate401 is then lifted axially away from plate 402 allowing the formed webmaterial to be removed from between plates 401 and 402.

FIG. 35 is an example of a continuous, dynamic press for intermittentlycontacting the moving web and forming a base material 406 into a formedweb material of the present invention. Polymeric film 406 is fed betweenplates 401 and 402 in a direction generally indicated by arrow 430.Plate 401 is secured to a pair of rotatably mounted arms 432, 434 whichtravel in a clockwise direction which move plate 401 in a clockwisemotion. Plate 402 is connected to a pair of rotary arms 436, 438 whichtravel in a counter clockwise direction moving plate 402 in a counterclockwise motion. Thus, as web 406 moves between plates 401 and 402 indirection indicated by arrow 430, a portion of the base film between theplates is formed and then released such that the plates 401 and 402 maycome together and form another section of base film 406. This method hasthe benefit of allowing virtually any pattern of any complexity to beformed in a continuous process, e.g., uni-directional, bi-directional,and multi-directional patterns.

The dynamic press of FIG. 35 could be used on a completed absorbentarticle to from strainable networks into the completed product. Forexample, the entire completed absorbent article could be placed betweenplates 401 and 402 to create a strainable network in all layers of theabsorbent article.

Another method of forming the base material into a web material of thepresent invention is vacuum forming. An example of a vacuum formingmethod is disclosed in commonly assigned U.S. Pat. No. 4,342,314, issuedto Radel et al. on Aug. 3, 1982. Alternatively, the formed web materialof the present invention may be hydraulically formed in accordance withthe teachings of commonly assigned U.S. Pat. No. 4,609,518 issued toCurro et al. on Sep. 2, 1986. Each of the above said patents beingincorporated herein by reference.

In FIG. 36 there is shown another apparatus generally indicated as 500for forming the base film into a formed web material of the presentinvention. Apparatus 500 includes a pair of rolls 502, 504. Roll 502includes a plurality of toothed regions 506 and a plurality of groovedregions 508 that extend substantially parallel to a longitudinal axisrunning through the center of the cylindrical roll 502. Toothed regions506 include a plurality of teeth 507. Roll 504 includes a plurality ofteeth 510 which mesh with teeth 507 on roll 502. As a base film ispassed between intermeshing rolls 502 and 504, the grooved regions 508will leave portions of the film unformed producing the first regions ofthe web material of the present invention. The portions of the filmpassing between toothed regions 506 and teeth 510 will be formed byteeth 507 and 510, respectively, producing rib-like elements in thesecond regions of the web material.

Alternatively, roll 504 may consist of a soft rubber. As the base filmis passed between toothed roll 502 and rubber roll 504 the film ismechanically formed into the pattern provided by the toothed roll 502.The film within the grooved regions 508 will remain unformed, while thefilm within the toothed regions 506 will be formed producing rib-likeelements of the second regions.

Referring now to FIG. 37, there is shown an alternative apparatusgenerally indicated as 550 for forming the based film into a formed webmaterial in accordance with the teachings of the present invention.Apparatus 550 includes a pair of rolls 552, 554. Rolls 552 and 554 eachhave a plurality of toothed regions 556 and grooved regions 558extending about the circumference of rolls 552, 554 respectively. As thebase film passes between rolls 552 and 554, the grooved regions 558 willleave portions of the film uniformed, while the portions of the filmpassing between toothed regions 556 will be formed producing rib-likeelements in second regions.

Web materials of the present invention may be comprised of polyolefinssuch as polyethylenes, including linear low density polyethylene(LLDPE), low density polyethylene (LDPE), ultra low density polyethylene(ULDPE), high density polyethylene (HDPE), or polypropylene and blendsthereof with the above and other materials. Examples of other suitablepolymeric materials which may also be used include, but are not limitedto, polyester, polyurethanes, compostable or biodegradable polymers,heat shrink polymers, thermoplastic elastomers, metallocenecatalyst-based polymers (e.g., INSITE® available from Dow ChemicalCompany and Exxact® available from Exxon), and breathable polymers. Theweb material may also be comprised of a synthetic woven, synthetic knit,nonwoven, apertured film, macroscopically expanded three-dimensionalformed film, absorbent or fibrous absorbent material, foam, filledcomposition, or laminates and/or combinations thereof. The nonwovens maybe made by but not limited to any of the following methods: spunlace,spunbond, meltblown, carded and/or air-through or calendar bonded, witha spunlace material with loosely bound fibers being the preferredembodiment.

While the present invention has been described as providing a webmaterial from a single layer of base film, the present invention may bepracticed equally well with other materials. While the fluid imperviouspolymeric film exhibiting an elastic-like behavior in the direction ofapplied elongation may be suitable for use a backsheet on a disposablediaper or sanitary napkin, such a web material would not function wellas a topsheet on an absorbent article. Examples of other base materialsfrom which the web of the present invention can be made and willfunction effectively as a fluid pervious topsheet on an absorbentarticle include two-dimensional apertured films and macroscopicallyexpanded, three-dimensional, apertured formed films. Examples ofmacroscopically expanded, three-dimensional, apertured formed films aredescribed in U.S. Pat. No. 3,929,135, issued to Thompson on Dec. 30,1975; U.S. Pat. No. 4,324,246 issued to Mullane, et al. on Apr. 13,1982; U.S. Pat. No. 4,342,314 issued to Radel, et al. on Aug. 3, 1982;U.S. Pat. No. 4,463,045 issued to Ahr, et al. on Jul. 31, 1984; and U.S.Pat. No. 5,006,394 issued to Baird on Apr. 9, 1991. Each of thesepatents are incorporated herein by reference.

Web materials of the present invention may include laminates of theabove mentioned materials. Laminates may be combined by any number ofbonding methods known to those skilled in the art. Such bonding methodsinclude but are not limited to thermal bonding, adhesive bonding (usingany of a number of adhesives including but not limited to sprayadhesives, hot melt adhesives, latex based adhesives and the like),sonic bonding and extrusion laminating whereby a polymeric film is castdirectly onto a substrate, and while still in a partially molten state,bonds to one side of the substrate, or by depositing meltblown fibersnonwoven directly onto a substrate.

The following are examples of specific embodiments of the presentinvention.

EXAMPLE 1

Two rigid plates similar to those of FIGS. 32 and 33 made by casting analuminum filled epoxy material onto a machined metal mold were made. Theouter dimensions of the plate are 5.0"×12"×0.75". On one surface of eachplate are a series of "teeth" which are substantially triangular incross section and measure 0.060" at these bases and taper to a vertexwith a radius of 0.008" at the top. The centerlines of the teeth arespaced evenly and at 0.060" increments. The plates have matching holesand pins through their thickness to ensure consistent mating of theplates when they are brought together. On the "toothed" side of oneplate a series of grooves are cut which are parallel to each other andperpendicular to the evenly spaced teeth. These grooves measure 0.065"in width and are continuous over the entire length of the plate, and arespaced at a distance of 0.50" on center. These grooves correspond to theundeformed regions of the deformed polymeric web.

A single thickness (0.001") of a polymeric film substantially comprisedof LLDPE which was made via the melt casting method is placed betweenthe two plates (one with grooves, one with only teeth). The plates withthe film between them are placed in a hydraulic press with platens whichare larger than the plates (to ensure that pressure is distributedevenly over the plates). At the edges of the plates are spacers whichcan vary in thickness to control the amount of interpenetration or"engagement" of the teeth. The plates are compressed between the platenof the press by a force of at least 4000 pounds which causes the regionsof the film between the mating teeth of the plates to be formed. Thefilm is left unformed in the regions corresponding to the grooves cut inone of the plates. The pressure is removed from the plates, and theformed web material is removed.

EXAMPLE 2

The plates described in Example 1 are used as described above. Thematerial to be deformed is made from one layer of a carded calendarbonded polypropylene nonwoven which is laminated, using a spray adhesivesuch as 3M "Super 77 Spray Adhesive" (any number of hot melt or pressuresensitive adhesives could also be used), to a 1 mil thick castpolyethylene film. The nonwoven material is very easily formed in thecross direction. The laminate is placed between the two deformationplates such that the cross direction of the nonwoven is parallel to thegrooves cut in the patterned plate. The resultant material has animproved aesthetic due to the lack of puckering upon release of theapplied strain (such as that seen in the material of Example 1).

Test Methods

Surface-Pathlength

Pathlength measurements of formed material regions are to be determinedby selecting and preparing representative samples of each distinctregion and analyzing these samples by means of microscopic imageanalysis methods.

Samples are to be selected so as to be representative of each region'ssurface geometry. Generally, the transition regions should be avoidedsince they would normally contain features of both the first and secondregions. The sample to be measured is cut and separated from the regionof interest. The "measured edge" is to be cut parallel to a specifiedaxis of elongation. Usually this axis is parallel to the formedprimary-axis of either the first region or the second region. Anunstrained sample length of one-half inch is to be "gauge marked"perpendicular to the "measured edge": while attached to the webmaterial, and then accurately cut and removed from the web material.

Measurement samples are then mounted onto the long-edge of a microscopicglass slide. The "measured edge" is to extend slightly (approximately 1mm) outward from the slide edge. A thin layer of pressure-sensitiveadhesive is applied to the glass face-edge to provide a suitable samplesupport means. For highly formed sample regions it has been founddesirable to gently extend the sample in its axial direction (withoutimposing significant force) simultaneous to facilitate contact andattachment of the sample to the slide-edge. This allows improved edgeidentification during image analysis and avoids possible "crumpled" edgeportions that require additional interpretation analysis.

Images of each sample are to be obtained as "measured edge" views takenwith the support slide "edge on" using suitable microscopic measuringmeans of sufficient quality and magnification. FIG. 38 shows a typicalview of a portion of the second region of a sample 900 having a firstside edge 901 and a second side edge 902 used to determine thesurface-pathlength. Data herein presented was obtained using thefollowing equipment, Keyence VH-6100 (20x Lens) video unit, withview-image prints made with a Sony Video printer Mavigraph unit. Videoprints were image-scanned with a Hewlett Packard ScanJet IIP scanner.Image analysis was on a MacIntosh IICi computer utilizing the softwareNIH MAC Image version 1.45.

Using this equipment, a calibration image initially taken of a gridscale length of 0.500" with 0.005" increment-marks to be used forcalibration setting of the computer image analysis program. All samplesto be measured are then video-imaged and video-image printed. Next, allvideo-prints are image scanned at 100 dpi (256-level gray scale) into asuitable Mac image-file format. Finally, each image-file (includingcalibration file) is analyzed utilizing Mac Image 1.45 computer program.All samples are measured with freehanded line-measurement tool selected.Samples are measured on both side-edges and the lengths are recorded.Simple film-like (thin & constant thickness) samples require only oneside-edge to be measured. Laminate and thick foam samples are measuredon both side-edges. Length measurement tracings are to be made along thefull gauge length of a cut sample. In cases of highly deformed samples,multiple (partially overlapping) images may be required to cover theentire cut sample. In these cases, select characteristic features commonto both overlapping-images and utilize as "markers" to permit imagelength readings to adjoin but not overlap.

The final determination of surface-pathlength for each region isobtained by averaging the lengths of five (5) separate 1/2"gauge-samples of each region. Each gauge-sample "surface-pathlength" isto be the average of both side-edge surface-pathlengths.

While the test method described above is useful for many of the webmaterials of the present invention it is recognized that the test methodmay have to be modified to accommodate some of the more complex webmaterials within the scope of the present invention.

Poisson's Lateral Contraction Effect

The Poisson's lateral contraction effect is measured on an Instron Model1122, as available from Instron Corporation of Canton, Mass., which isinterfaced to a Gateway 2000 486/33 Hz computer available from Gateway2000 N. Sioux City, S.Dak., using Test Works™ software which isavailable from Sintech, Inc. of Research Triangle Park, N.C. Allessential parameters needed for testing are input in the TestWorks™software for each test. Data collection is accomplished through acombination of manual sample width measurements, and elongationmeasurements made within TestWorks™.

The samples used for this test are 1" wide×4" long with the long axis ofthe sample cut parallel to the direction of the first region of thesample. The sample should be cut with a sharp knife or suitably sharpcutting device designed to cut a precise 1" wide sample. It is importantthat a "representative sample" should be cut so that an arearepresentative of the symmetry of the overall pattern of the deformedregions is represented. There will be cases (due to variations in eitherthe size of the deformed portion or the relative geometries of regions 1and 2) in which it will be necessary to cut either larger or smallersamples that is suggested herein. In this case, it is very important tonote (along with any data reported) the size of the sample, which are ofthe deformed region it was taken from and preferably include a schematicof the representative are used for the sample. In general, an "aspectratio" of (2:1) for the actual extended tensile portion (l1:w1) is to bemaintained if possible. Five samples are tested.

The grips of the Instron consist of air actuated grips designed toconcentrate the entire griping force along a single line perpendicularto the direction of testing elongation having one flat surface and anopposing face from which protrudes a half round. No slippage should bepermitted between the sample and the grips. The distance between thelines of gripping force should be 2" as measured by a steel rule heldbeside the grips. This distance will be referred to from here on as the"gauge length".

The sample is mounted in the grips with its long axis perpendicular tothe direction of applied elongation. An area representative of theoverall pattern geometry should be symmetrically centered between thegrips. The crosshead speed is set to 10 in/min. The crosshead moves tothe specified strain (measurements are made at both 20 and 60%elongation). The width of the sample at its narrowest point (w2) ismeasured to the nearest 0.02" using a steel rule. The elongation in thedirection of applied extension is recorded to the nearest 0.02" on theTestWorks software. The Poisson's Lateral Contraction Effect (PLCE) iscalculated using the following formula ##EQU4## where w2=The width ofthe sample under an applied longitudinal elongation; w1=The originalwidth of the sample;

l2=The length of the sample under an applied longitudinal elongation;and

l1=The original length of the sample (gauge length);

Measurements are made at both 20 and 60% elongation using five differentsamples for each given elongation. The PLCE at a given percentelongation is the average of five measurements.

While the test method described above is useful for many of the webmaterials of the present invention it is recognized that the test methodmay have to be modified to accommodate some of the more complex webmaterials within the scope of the present invention.

Hysteresis Test

The hysteresis test is used for measuring the percent set and percentforce relaxation of a material. The tests are performed on an InstronModel 1122, available from Instron Corporation of Canton, Mass. which isinterfaced to a Gateway 2000 486/33 Hz computer available from Gateway2000 of N. Sioux City, S.Dak. 57049, using TestWorks™ software which isavailable from Sintech, Inc. of Research Triangle Park, N.C. 27709. Allessential parameters needed for testing are input in the TestWorks™software for each test (i.e. Crosshead Speed, Maximum percent elongationPoint and Hold Times). Also, all data collection, data analysis andgraphing are done using the TestWorks™ software.

The samples used for this test are 1" wide×4" long with the long axis ofthe sample cut parallel to the direction of maximum extensibility of thesample. The sample should be cut with a sharp exacto knife or somesuitably sharp cutting device design to cut a precise 1" wide sample.(If there is more than one direction of elongation of the material,samples should be taken parallel to representative directions ofelongation). The sample should be cut so that an area representative ofthe symmetry of the overall pattern of the deformed region isrepresented. There will be cases (due to variations in either the sizeof the deformed portion or the relative geometries of the first andsecond regions) in which it will be necessary to cut either larger orsmaller samples than is suggested herein. In this case, it is veryimportant to note (along with any data reported) the size of the sample,which area of the deformed region it was taken from and preferablyinclude a schematic of the representative area used for the sample.Three separate tests at 20, 60 and 100% strain are typically measuredfor each material. Three samples of a given material are tested at eachpercent elongation.

The grips of the Instron consist of air actuated grips designed toconcentrate the entire gripping force along a single line perpendicularto the direction of testing stress having one flat surface and anopposing face from which protrudes a half round to minimize slippage ofthe sample. The distance between the lines of gripping force should be2" as measured by a steel rule held beside the grips. This distance willbe referred to from hereon as the "gauge length". The sample is mountedin the grips with its long axis perpendicular to the direction ofapplied percent elongation. The crosshead speed is set to 10 in/min. Thecrosshead moves to the specified maximum percent elongation and holdsthe sample at this percent elongation for 30 seconds. After the thirtyseconds the crosshead returns to its original position (0% elongation)and remains in this position for 60 seconds. The crosshead then returnsto the same maximum percent elongation as was used in the first cycle,holds for thirty seconds and then again returns to zero.

A graph of two cycles is generated. A representative graph is shown inFIG. 7. The percent force relaxation is determined by the followingcalculation of the force data from the first cycle: ##EQU5## The percentset is the percent elongation of the sample of the second cycle wherethe sample starts to resist the elongation. The percent set and thepercent force relaxation are shown graphically also in FIGS. 7, 9, 11,13 and 15. The average percent force relaxation and percent set forthree samples is reported for each maximum percent elongation valuetested.

While the test method described above is useful for many of the webmaterials of the present invention it is recognized that the test methodmay have to be modified to accommodate some of the more complex webmaterials within the scope of the present invention.

Tensile Test

The tensile test is used for measuring force versus percent elongationproperties and percent available stretch of a material. The tests areperformed on an Instron Model 1122, available from Instron Corporationof Canton, Mass. which is interfaced to a Gateway 2000 486/33 Hzcomputer available from Gateway 2000 N. Sioux City, S.Dak., usingTestWorks™ software which is available from Sintech, Inc. of ResearchTriangle Park, N.C. All essential parameters needed for testing areinput in the TestWorks™ software for each test. Also, all datacollection, data analysis and graphing are done using the TestWorks™software.

The samples used for this test are 1" wide×4" long with the long axis ofthe sample cut parallel to the direction of maximum extensibility of thesample. The sample should be cut with a sharp exacto knife or somesuitably sharp cutting device design to cut a precise 1" wide sample.(If there is more than one direction of extensibility of the material,samples should be taken parallel to representative direction ofelongation). The sample should be cut so that an area representative ofthe symmetry of the overall pattern of the deformed region isrepresented. There will be cases (due to variation in either the size ofthe deformed portion or the relative geometries of regions 1 and 2) inwhich it will be necessary to cut either larger or smaller samples thanis suggested herein. In this case, it is very important to note (alongwith any data reported) the size of the sample, which area of thedeformed region it was taken from and preferably include a schematic ofthe representative area used for the sample. Three samples of a givenmaterial are tested.

The grips of the Instron consist of air actuated grips designed toconcentrate the entire gripping force along a single line perpendicularto the direction of testing stress having one flat surface and anopposing face from which protrudes a half round to minimize slippage ofthe sample. The distance between the lines of gripping force should be2" as measured by a steel rule held beside the grips. This distance willbe referred to from hereon as the "gauge length". The sample is mountedin the grips with its long axis perpendicular to the direction ofapplied percent elongation. The crosshead speed is set to 10 in/min. Thecrosshead elongates the sample until the sample breaks at which pointthe crosshead stops and returns to its original position (0%elongation).

Graphs of the tensile data are shown in FIGS. 6, 8, 10, 12 and 14. Thepercent available stretch is the point at which there is an inflectionin the force--elongation curve, beyond which point there is a rapidincrease in the amount of force required to elongate the sample further.This point is shown graphically in FIGS. 6, 8, 10, 12 and 14. Theaverage of the percent available stretch for three samples is recorded.

While the test method described above is useful for many of the webmaterials of the present invention it is recognized that the test methodmay have to be modified to accommodate some of the more complex webmaterials within the scope of the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodification that are within the scope of this invention.

What is claimed is:
 1. A method for forming a web material into a webmaterial exhibiting an elastic-like behavior in response to an appliedelongation along at least one axis thereof, said web material comprisinga strainable network having first and second regions, said first regionproviding a first, elastic-like resistive force to the appliedelongation, and the second region providing a second resistive force tofurther applied elongation, said method comprising the steps of:a)providing a web material; and b) feeding said web material between afirst roll and a second roll, said first roll comprising a plurality oftoothed regions spaced apart by a plurality of grooved regions, saidtoothed regions comprising a plurality of teeth, said second rollcomprising a plurality of teeth which mesh with said teeth on said firstroll, as said web material is fed between said first roll and saidsecond roll the portion of said web material passing between the teethon said first roll and the teeth on said second roll being formed intosaid second regions of said web material while the portion of said webmaterial passing between the grooves on said first roll and the teeth onsaid second roll being formed into said first regions of said webmaterial.